Reactive liquid ceramic binder resin

ABSTRACT

A reactive liquid ceramic binder suitable for the production of ceramic products from ceramic powders is provided. The reactive liquid ceramic binder contains organo-modified siloxane compounds, wherein the liquid organo-modified siloxane compounds contain organoalkoxysiloxane units according to general formula (I) 
     
       
         
         
             
             
         
       
     
     wherein
         R 1 =alkyl radical and/or aryl radical,   R 2 =H and/or alkyl radical with 1 to 4 carbon atoms,   a≧0 and ≦2, and   b&gt;0 and ≦3,
 
with the proviso that a+b≧1 and ≦4.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/789,982, filed Apr. 26, 2007, the entire content and disclosure ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a reactive liquid binder, which issuitable for the binding of ceramic particles for the production ofceramic products, in particular refractory ceramic products, fromceramic powders. The invention further relates to the use of the binderand a process for the production of the aforesaid ceramic products, andalso ceramic products as such, wherein refractory ceramic products areparticularly preferred according to the invention.

BACKGROUND OF THE INVENTION

Refractory ceramic products, also referred to below as “refractories”,are used for protection against high temperatures in many industrialplants. The most important refractory material types are:

-   -   shaped dense products, with a porosity≦45 vol.%, such as bricks        and building components,    -   shaped thermally insulating products, with a porosity≧45 vol.%,        such as lightweight refractory bricks,    -   unshaped refractory products, such as refractory concretes,        ramming mixes, spraying mixes and the like.

Conventional refractory products are produced from powder raw materials.The grain size of the powder lies in a relatively broad range, between afew micrometers up to several millimeters. In isolated cases, rawmaterials with a particle size>10 mm are also used. Correspondingly, thepowders are described as coarse-grained, medium-grained, fine-grainedand ultra fine-grained particle fraction.

From the state of the art, solid, branched or cross-linked, highmolecular weight organo-modified siloxanes or solidphenylmethylpolysiloxanes are known.

WO 93/01146 relates to a binder for thermoplastic molding mixescontaining at least one thermoplastic silicone resin, with a softeningpoint between 30° C. and 200° C., for the production of molded partsfrom ceramic or metal from the corresponding ceramic or metal powders.Such thermoplastic molding mixes are used inter alia in processes suchas ceramic injection moulding, extrusion or hot pressing, whereintemperature-dependent flow behavior is necessary. Such silicone resinsare according to WO 93/01146 preferably used without catalysts, so thatfurther cross-linking and curing during the molding process does notoccur.

The use of these aforesaid solid siloxane compounds as ceramic bindershas the disadvantage that very homogenous mixtures with ceramicmaterials are inadequately produced or they are not produced at all.Moreover, with the use of such binders, a sufficiently high greenstrength of the ceramic product molded from ceramic particles cannot beobtained without a heat treatment at higher temperatures. A furtherdisadvantage of prior art binders is that very high firing temperatures,usually over 1000° C., are needed in order to obtain refractory ceramicproducts with adequate mechanical properties such as cold crushingstrength. Moreover, high pressures and long firing times are needed,which is associated with high energy consumption.

Furthermore, WO 93/01146 relates to a binder for thermoplastic moldingmixes, wherein the molding mixes are exclusively processed plasticallyabove the softening point of the silicone resin, and introduced underpressure into molds whose temperature lies below the softening point ofthe silicone resin. According to the teaching of WO 93/01146, molded,ceramic products with adequate green strength cannot be produced bynon-plastic processing, for example uniaxially or isostatically pressed,by slip casting, by ramming, or spraying, in particular at temperaturesbelow the softening point of the silicone resin or the like. Inaddition, unshaped ceramic products, in particular refractory materials,cannot be produced with the binder and process described in WO 93/01146.

In view of the above, there is a need for a reactive liquid binder thatovercomes the drawbacks of prior art binders discussed above, whichbinder can be used for the binding of ceramic particles for theproduction of ceramic products.

SUMMARY OF THE INVENTION

Surprisingly, it has now been found that ceramic products, in particularrefractory ceramic products which have unexpectedly high cold crushingstrength, can be obtained at low treatment temperatures.

The aforementioned objective is achieved in the present invention bymeans of a reactive liquid ceramic binder, which is suitable for theproduction of ceramic products, in particular refractory ceramicproducts, from ceramic powders, wherein the reactive liquid ceramicbinder contains at least one organo-modified siloxane compound, whereinthe at least one organo-modified siloxane compound containsorganoalkoxysiloxane units according to general formula (I)

wherein

R¹=alkyl radical and/or aryl radical,

R²=H and/or alkyl radical with 1 to 4 carbon atoms,

a≧0 and ≦2, and

b>0 and ≦3,

with the proviso that a+b≧1 and ≦4.

The invention further relates to the use of the inventive binderdescribed above as well as a process for the production of ceramicproducts, and also ceramic products as such, wherein refractory ceramicproducts are particularly preferred according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, the sole FIGURE present in the instant application, shows theeffects of the firing temperature on the cold crushing strength ofceramic samples with and without the addition of compound A which is acompound within the scope of formula (I).

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a reactive liquid ceramic binder,which is suitable for the production of ceramic products, in particularrefractory ceramic products, from ceramic powders, will now be describedin greater detail.

As stated above, the present invention provides a reactive liquidceramic binder that contains at least one organo-modified siloxanecompound, wherein the at least one organo-modified siloxane compoundcontains organoalkoxysiloxane units according to general formula (I)

wherein

R¹=alkyl radical and/or aryl radical,

R²=H and/or alkyl radical with 1 to 4 carbon atoms,

a≧0 and ≦2, and

b>0 and ≦3,

with the proviso that a+b≧1 and ≦4.

Formula (I) is an average formula of the organoalkoxy-siloxane units ofthe liquid, organo-modified siloxane compound.

The proportion of H for R² can be ≧0% and ≦10%, preferably ≧0% and ≦5%,particularly preferably ≧0% and ≦1%, and especially preferably 0%.

The term “ceramic product” includes inter alia ceramic mixes,dimensionally stable ceramic objects and refractory ceramic products.

The inventive reactive liquid ceramic binder preferably contains atleast one liquid organo-modified siloxane compound, wherein the liquid,organo-modified siloxane compound contains organoalkoxysiloxane unitsaccording to the general formula (I).

The term “liquid” as used in the present invention has the meaning thatthe corresponding substance, in particular the liquid, organo-modifiedsiloxane compound or the corresponding mixture is liquid at roomtemperature, i.e. 25° C.

Preferably, the substituents R¹ and/or R² of the organoalkoxysiloxanesof the liquid, organo-modified siloxane compound/s are as defined below:

-   R¹=phenyl and/or C₁-C₁₆ alkyl radical, preferably R¹=C₁-C₁₂ alkyl    radical, more preferably R¹=C₁-C₈ alkyl radical, particularly    preferably R¹=C₁-C₄ alkyl radical, wherein most preferably R¹=methyl    and/or ethyl; and/or-   R²=H, methyl, ethyl, propyl, isopropyl, butyl or tert-butyl, where    methyl and/or ethyl are most preferred.

Furthermore, it is preferable according to the invention that a=0.5 to1.8, preferably a=0.7 to 1.7, and more preferably a=1.0 to 1.5, with theproviso that a+b≦4 and preferably a+b≦3.

In addition, it is also specified according to the invention that b=0.1to 2.5, preferably b=0.2 to 2.3, still more preferably b=>0.3 to 2.0 andparticularly preferably b=>0.3 to 1.2, with the proviso that a+b≦4 andpreferably a+b≦3.

The reactive liquid organo-modified siloxane compounds according to theinvention can have a molecular weight from 120 to 100,000, preferably250 to 80,000, preferably 500 to 60,000, more preferably 750 to 50,000and particularly preferably 1,000 to 30,000.

Moreover, the reactive liquid ceramic binder according to the inventioncan contain a solvent selected from organic solvents, preferably liquidhydrocarbons, in particular with a boiling point between 40° C. to 100°C., alcohol and/or acetone. Through the addition of solvents, forexample, the miscibility with ceramic powders can be improved.

In some embodiments of the present invention, it is preferable that thereactive liquid ceramic binder, in particular a ceramic bindercontaining liquid organo-modified siloxane compounds, is used in amixture with water, preferably as an aqueous emulsion. Through the useof an aqueous emulsion in combination with the ceramic powder, forexample, a material that can be cast or sprayed at room temperature canbe produced.

For the improvement of the properties for example with regard toprocessability, handling, drying process, firing process, strength,corrosion resistance and/or oxidation resistance of the ceramic mixand/or ceramic product, at least one additive can be added to theceramic binder, wherein this additive is different from theorgano-modified siloxane compound(s) based on the formula (I) and isselected from an inorganic binder, an inorganic salt of sulfuric acid,an inorganic salt of hydrochloric acid, an inorganic salt of phosphoricacid, magnesium chloride, magnesium sulfate, monoaluminum phosphate,alkali metal phosphate, alkali metal silicate, waterglass, an organicbinder resin, cellulose derivative, polyvinyl alcohol, water, organicsolvents, mold release agents, stabilizers, organic pigments, inorganicpigments, non-oxide substances, preferably carbon, metal powders, metalfibers, ceramic fibers, glass fibers, natural fibers, plastic fibers,metal oxides, borides, carbides, nitrides, oxynitrides, oxycarbides,silicides, polymers, catalyst and/or carbon fibers. The addition of veryreactive nanoscale, oxide and/or non-oxide powders can be preferable insome embodiments and the addition of nano-aluminum oxide and/or ofprecursors thereof can be particularly preferable in yet otherembodiments.

Further additives which are usable according to the invention, inparticular for the improvement of the processability, handling, greendensity, green strength etc., include setting retardants, settingaccelerators, pressing agents, lubricants, set-up agents, antifoamagents, liquefiers, sintering agents and the like.

Particularly preferred is the use of liquid, organo-modified siloxanecompounds of the binder according to the invention in combination withother additives, such as organic and/or inorganic binders, water,organic solvents, functional additives such as carbon, borides, metalpowders, carbides, silicides, oxides and the like.

Likewise, the use of the ceramic binder in combination with hydraulicbinders, such as hydratable aluminum oxide, calcium aluminate cement,Portland cement, or gypsum optionally with water in variable amounts,can be advantageous.

In some embodiments, nanoscale metal oxides, preferably nanoscalealuminum oxide, can be added to the ceramic binder, which can result inimproved cold crushing strength of ceramic products.

Furthermore, it has surprisingly been found that the use of theinventive reactive liquid ceramic binder in combination with a ceramicpowder leads to stable, in particular refractory, ceramic products withlow firing temperatures.

In general and in the description of the present invention, refractoryceramic products are also described as refractory ceramic materials orrefractories.

A further advantage of the present invention is that ceramic productswith adequate green strength can be produced by use of the inventivereactive liquid ceramic binder at temperatures<30° C., preferably atroom temperature.

It is advantageous that through the use of the ceramic binder accordingto the invention, the firing temperature and/or the firing time andhence the energy consumption in the production of ceramic products, inparticular refractory products, can be decreased. In addition, with theuse of fossil energy sources, CO₂ and NO_(x) emission can be reduced onaccount of the lower energy consumption.

It has also been observed that the firing times can be shortened, atleast in most cases, without this being disadvantageous with regard tothe material properties, in particular the strength, of the ceramicproducts produced using the inventive ceramic binder compared toconventional refractory ceramic products, i.e., those produced accordingto the state of the art.

Furthermore, it has advantageously been observed that on use of thereactive liquid ceramic binder according to the invention in thetemperature range between, for example, 100° C. and 1000° C., preferably200° C. and 800° C., there is no decrease, or only a slight decrease, inthe material strength, i.e., the cold crushing strength.

The use of the reactive liquid ceramic binder according to the inventioncan result in no formation or no significant formation of low-meltingphases in the ceramic during the production process. This isadvantageous, since the occurrence of such phases is disadvantageous forthe material properties, in particular with regard to their stability athigh temperatures.

Yet another advantage of the reactive liquid ceramic binder of theinstant invention is that with or without the addition of water itimparts high dimensional stability to the ceramic product, and istherefore preferably also usable for ceramic products susceptible tohydration, for example basic refractories.

In the meaning of this invention, ceramic products also include dried,annealed and/or fired ceramic products. The term ceramic product, asused in the present description, also includes so-called green bodies.In particular, the term ceramic product includes heat-resistant and/orrefractory ceramic products (refractories). Furthermore, a ceramicproduct is also understood to mean products such as molded objects andmaterials wherein a so-called composite material is involved, i.e.,which are made up of a ceramic material and at least one other materialor other phase. This can also be present as at least one ceramic layer,preferably a ceramic surface coating.

By means of the reactive liquid ceramic binder according to theinvention, shaped and unshaped ceramic products, in particularheat-resistant and/or refractory, unfired and/or fired ceramic shapedobjects, unshaped refractory products, for example concretes, rammingmixes, casting mixes, coatings or coverings with excellent physical andmechanical properties and improved production parameters can beobtained.

According to the invention, production parameters should be understoodto mean in particular the parameters for the production of the unshapedproducts, the unfired products, the green bodies, and the fired ceramicproducts.

The reactive liquid ceramic binder according to the invention can beadded to the ceramic powder in a weight proportion of 0.01 wt. % to 70wt. %, preferably from 0.1 wt. % to 50 wt. % and even more preferablyfrom 0.5 wt. % to 30 wt. % based on the total weight of the ceramicpowder.

It has surprisingly been found that the reactive liquid ceramic binderis effective in markedly lower proportions, based on the ceramic powder,than the compounds known from the state of the art. Marked effects canbe achieved with proportions of the organo-modified siloxane compoundsof less than 5 wt. %, based on the total weight of the ceramic powder.According to the invention, proportions of the organo-modified siloxanecompounds in the range from 0.05 wt. % to <10 wt. %, in particular 0.1wt. % to 5 wt. %, particularly preferably 0.5 wt. % to 3 wt. %, eachbased on the quantity of ceramic powder, are preferred.

If the proportion of the organo-modified siloxane compounds added isbelow 0.01 wt. %, it is very difficult to obtain a fired product of highstrength, while with the addition of more than 10 wt. %, in particularmore than 15 wt. % of the organo-modified siloxane compounds, swellingof the fired product can be observed, as a result of which its strengthand density can be adversely affected.

According to the invention, the reactive liquid ceramic binder can beused for the production of ceramic products, in particular of shaped andunshaped, fired and unfired refractory, ceramic products, from ceramicpowder/s.

A further object of the present invention relates to a ceramic mixturewhich contains ceramic binder according to the invention and ceramicpowder.

The ceramic mixtures can be used directly, or firstly be processed intopowders or granulates.

Surprisingly, it has also been found that ceramic mixes containing theliquid organo-modified siloxane compounds can be processed attemperatures below the softening point of solid, organo-modifiedsiloxane compounds.

According to the invention, it can therefore be preferable to processceramics containing ceramic powder and ceramic binder merely underpressure.

The ceramic mixes according to the invention can be used for theproduction of shaped and unshaped ceramic products, and for theproduction of fired and also unfired ceramic products.

Preferably, ceramic powders usable for the production of the ceramicmixtures can be selected from the group comprising coarse-grained,medium-grained, fine-grained and/or ultrafine-grained ceramic particles.Suitable ceramic particles can include all typical, oxide, non-oxide,acidic or basic ceramic raw materials and mixtures thereof. Particularlypreferred are Al₂O₃-based ceramic products. Mixtures of these rawmaterials can also be present.

Ceramic powders, in particular mixtures of ceramic powders and rawmaterials thereof particularly suitable for use, include:

-   -   Oxides, such as BeO, MgO, Al₂O₃, SiO₂, CaO, TiO₂, Cr₂O₃, MnO,        Fe₂O₃, ZnO, SrO, Y₂O₃, BaO, CeO₂ and UO₂; and/or    -   Carbides, such as Be₂C, Be₄C, Al₄C₃, SiC, TiC, Cr₃C₂, Mn₃C,        Fe₃C, SrC₂, YC₂, ZrC, NbC, Mo₂C, BaC₂, CeC₂, HfC, TaC, WC and        UC; and/or    -   Nitrides, such as Be₃N₂, BN, Mg₃N₂, AlN, Si₃N₄, Ca₃N₂, TiN, VN,        CrN, Mn₃N₂, Sr₃N₂, ZrN, NbN, Mo₃N₂, HfN, TaN, WN₂ and UN; and/or    -   Borides, such as AlB₄, CaB₆, TiB₂, VB₂, CrB₂, MnB, FeB, CoB,        NiB, SrB₆, YB₆, ZrB₂, NbB₂, MoB₂, BaB₆, LaB₆, CoB₆, HfB₂, TaB₂,        WB and UB₄; and/or    -   Silicides, such as CaSi, Ti₅Si₃, V₅Si₃, CrSi₂, FeSi, CoSi,        ZrSi₂, NbSi₂, MoSi₂, TaSi₂ and WSi₂; and/or    -   mixtures of the aforesaid ceramic substances.

Further ceramic particles which can be used include oxide and non-oxidecompounds, mixed phases and the like, for example mullite (Al₆Si₂O₁₃),mixed crystals from the Al₂O₃—Cr₂O₃ system, MgSiO₄, CaSiO₄, ZrSiO₄,MgAl₂O₄, CaZrO₃, SIALON, ALON, and/or B₄C—TiB₂.

In addition, ceramic particles of non-stoichiometric composition such asTiOx silicates, glasses and ceramic materials with a metal phase can beused according to the invention.

Ceramic particles usable according to the invention can also includecalcined aluminas, reactive aluminas, ultrafine-milled refractory rawmaterials such as microsilica, refractory clay and/or bond clay.

In the meaning of the present invention, coarse-grained is understood tomean granulations preferably ≧1 mm, particularly preferably 1 mm to 10mm. In the meaning of the present invention, medium-grained isunderstood to mean granulations from ≧0.1 mm to ≦1 mm, preferably 0.2 mmto 0.5 mm.

In the meaning of the present invention, fine-grained is understood tomean granulations from 0.02 mm to ≦0.2 mm, particularly preferably 0.02mm to 0.1 mm. This granulation fraction is commonly also referred to intechnical language as flour.

Ultrafine granules is understood to mean in particular reactiverefractory components with an average particle size≦15 μm, preferably ≦5μm.

For the attainment of good strength properties in the ceramic productsaccording to the invention, the use of ceramic mixes containing theceramic binder in combination with so-called functional additives suchas oxide and/or non-oxide micropowders, nanopowders, metal powders,metal, ceramic, glass or plastic fibers and/or fabrics can beadvantageous.

It is particularly preferable if the ceramic mixture contains nanoscalemetal oxides, preferably nanoscale aluminum oxide.

For some process steps and/or applications, it has been foundadvantageous in some instances to use or to use in part grain sizes lessthan 1 μm, in other words to add nanoscale ceramic powders to theceramic powder mixture.

The coarse-grained components can be present in the ceramic material inproportions≦100 wt. %, preferably in proportions≦90 wt. %, particularlypreferably in proportions from 15 wt. % to 80 wt. %, based on the totalweight of the ceramic mixture.

The medium-grained components can be present in the ceramic mix inproportions 100 wt. %, preferably in proportions 40 wt. %, particularlypreferably in proportions from 3 wt. % to 20 wt. %, based on the totalweight of the ceramic mix.

The fine-grained components can be present in the ceramic mix inproportions 100 wt. %, preferably in proportions≦95 wt. %, particularlypreferably in proportions from 5 wt. % to 80 wt. %, based on the totalweight of the ceramic mix.

The ultrafine-grained components can be present in the ceramic mix inproportions 100 wt. %, preferably in proportions≦50 wt. %, particularlypreferably in proportions from 0.1 wt. % to 35 wt. %, based on the totalweight of the ceramic mix.

The term “total weight of the ceramic mix” as used above relates to theceramic mix without binder.

Furthermore, it is preferable that the ceramic mix be free-flowing. Theceramic mix can have a powder density of 500 g/l to 2000 g/l, preferablyfrom 600 g/l to 1800 g/l, more preferably from 700 g/l to 1600 g/l,preferably from 800 g/l to 1500 g/l and particularly preferably from 850g/l to 1200 g/l.

Furthermore, additives, additive substances and/or binders, selectedfrom the group comprising organic binders, inorganic binders, water andthe like can be added to the ceramic mix.

The ceramic mix according to the invention can be in the form of a spraymolding mix, ramming mix, molding mix, painting mix or coating mix.

The ceramic powder can contain grain sizes in the nano range and canpreferably consist of oxides, carbides, nitrides, borides and/orsilicides, preferably oxides of aluminum.

The ceramic mix obtained can be used directly for the process accordingto the invention, however it can also be calcined in air, under vacuumor in an atmosphere of inert gas, carbon monoxide, carbon dioxide,nitrogen and/or hydrocarbons and the calcined molding mix pulverized andused as a ceramic, preferably nanoscale, powder.

Particularly preferably are ceramic mixes which contain ceramic powderssuch as magnesium silicates, aluminum silicates, spinets, silicondioxide, magnesium oxide, calcium oxide, chromium oxide, aluminum oxide,zirconium oxide, zinc oxide, zirconium silicate, silicon carbide,SIALON, ALON, silicon nitride and/or mixtures thereof.

The ceramic mixes can also contain catalysts, normal additivesubstances, binders and/or additives. The ceramic mixes can also containsmall quantities of mold release agents, stabilizers and/or pigments.

Furthermore, the use of ceramic mixes containing the ceramic binder incombination with hydraulic binders such as alumina cement or Portlandcement, optionally with water in variable quantities, can likewise beadvantageous.

A further object of the present invention relates to a process for theproduction of ceramic products, in particular of refractories.

The process according to the invention for the production of moldedceramic products can quite generally be divided into two embodiments.

In the first embodiment, the molding mix, which is a mixture of theceramic powder and the binder according to the invention, is firstlycompressed under a compression pressure of >1 MPa, preferably between≧100 MPa and ≦200 MPa, in order to produce a molded blank or green bodyof a defined external shape. The pressing can be effected by means ofconventional technologies, for example uniaxially, isostatically or thelike. The resulting ceramic body can be fed into the application withouta further heat treatment or can be subjected to a subsequent firing,whereby a ceramic product, preferably a refractory ceramic product, isobtained.

According to the second embodiment, the mixture of the ceramic powderand the reactive liquid binder according to the invention issimultaneously molded and heated and/or fired (so-called hot pressingprocess). In this embodiment of the present invention, the mixture iscompressed under a compression pressure of >1 MPa, preferably 5 MPa to100 MPa, at a higher temperature than room temperature, preferably >50°C. The pressing can be effected by means of conventional technologies,for example uniaxially, isostatically or the like. The resulting ceramicbody can be fed into the application without a further heat treatment orcan be subjected to a subsequent firing, whereby a ceramic product,preferably a refractory ceramic product, is obtained.

A suitable process for the production of shaped ceramic products, inparticular shaped refractory ceramic products, comprises the followingsteps:

-   -   a) mixing of a reactive liquid ceramic binder according to the        invention with ceramic powder so as to create a molding mix, and    -   b) consolidation of the molding mix obtained from step a) by        means of pressure treatment and/or heat treatment, whereby a        dimensionally stable ceramic product is obtained.

A further process for the production of unshaped ceramic products, inparticular refractory ceramic products, comprises the following steps:

-   -   a) mixing of a ceramic binder according to the invention with        ceramic powder;    -   b) optionally addition of additives, auxiliary agents and/or        additive substances and/or other binders; and    -   c) creation of a ceramic compound, such as a concrete compound,        molding mix, tamping mix or ramming mix.

The reactive liquid ceramic binder, in particular the liquidorgano-modified siloxane compound, can be contained in the molding mixor ceramic mix in a weight proportion of 0.01 wt. % to 70 wt. %,preferably from 0.1 wt. % to 50 wt. % and preferably from 0.5 wt. % to30 wt. %, based on the total weight of the ceramic powder.

To produce composite materials, the mixture obtained from step a) of theprocess can be applied onto a dimensionally stable support. Next theceramic mix can be dried and/or annealed and/or fired. The thermalstability and/or size of the support material is inter alia decisive asto whether the composite material is only dried or exposed to furtherheat treatment steps such as annealing and/or firing.

As described above, an additive substance and/or binder can be added tothe ceramic powder in a weight proportion from 0.01 wt. % to 50 wt. %,preferably from 0.05 wt. % to 30 wt. % and preferably from 0.1 wt. % to20 wt. % based on the total weight of the ceramic powder.

Preferably the green body obtained from step b) can be consolidated by

-   -   drying the green body at a temperature of ≧25° C. to        <200° C.; and/or    -   annealing at a temperature of ≧200° C. to ≦1000° C.; and/or    -   firing at a temperature of ≧1000° C.

In the production of refractory products it can be important that theceramic binder containing liquid organo-modified siloxane compounds usedaccording to the invention reacts with other components of the ceramicmix, preferably of the refractory ceramic mix during the heat treatment,with the formation of refractory compounds.

In refractory ceramic mixes which produce no strength or only inadequatestrength with the added liquid organo-modified siloxane compounds, anadequate binding strength can be attained by addition of an activeceramic powder. Particularly suitable for such a purpose is aluminumoxide. Also suitable are Al-containing substances which form a reactivealuminum oxide after a conversion process, for example, oxidation.

The reaction responsible for the bonding between ceramic powder and theorgano-modified siloxane compounds of the reactive liquid ceramic binderaccording to the invention can take place at room temperature. Withincreasing temperature, the bonding strengthens further. After a heattreatment in the medium temperature range, from 400° C. to 1000° C. orto some extent even from 200° C. to 600° C., the ceramic products, inparticular ceramic refractory materials, can reach high strengths, as aresult of which a high temperature firing of >1000° C. is not necessary.

The strength of the dried and/or annealed and/or fired molded object canbe further increased by impregnating it at least once with:

-   -   organo-modified siloxane compounds of the reactive liquid        ceramic binder according to the invention, in particular with        liquid, organo-modified siloxane compounds; and/or    -   a liquid polymeric organosilicon compound; and/or    -   with a solution of a solid polymeric organosilicon compound in a        solvent; and/or    -   with a melt of a solid polymeric organosilicon compound;        at room temperature and/or with heating and heated to a        temperature of ≧200° C. in air, under vacuum and/or in an        atmosphere of inert gas, hydrogen, carbon monoxide, carbon        dioxide, nitrogen and/or hydrocarbons, after the impregnation        level has if necessary been raised by increasing the pressure.

The addition of a solvent to the ceramic binder resin to decrease theviscosity can favor the impregnation process.

A molded blank is understood to mean a usable green body, which hassufficient initial strength for it to be capable of being handled ormechanically processed in further process steps.

In addition, green bodies can be cured before the sintering in order toobtain still stronger green bodies. The curing can be effected by:

-   -   ageing in a moist atmosphere, and/or    -   heating to a temperature 30° C., and/or    -   addition of suitable condensation catalysts, known per se, such        as dibutyltin dilaurate or tetrabutyl titanate.

Through the use of the ceramic binder according to the invention, inparticular ceramic binder wherein the reactive liquid ceramic bindercontains liquid organo-modified siloxane compounds, an adequately highgreen strength can be attained. The high dimensional stability or coldcrushing strength makes it possible for the green bodies to be furtherprocessed or molded before the final annealing or firing process,without this resulting in destruction of the green bodies owing tomechanical stress.

The green bodies can be molded by normal processes known in the state ofthe art. The molded green bodies can, if desired, be further shaped bymechanical processing.

The firing of the molded bodies or of the ceramic products can becontinued until no further weight loss is observed. The duration of thefiring process varies depending on the temperature, the composition ofthe molding mix and the proportion of the siloxanes used according tothe invention in the molding mix.

Constant weight is normally reached after 1 to 24 hours attemperatures>400° C.

Surprisingly it has now been found that with the use of the ceramicbinder according to the invention, in particular ceramic binder whereinthe reactive liquid ceramic binder preferably contains liquidorgano-modified siloxane compounds, and of molding mixes according tothe invention containing the reactive liquid ceramic binder, a firing offracture-free ceramic products with outstanding physical and mechanicalproperties can be achieved:

-   -   in a shorter time relatively at the same firing temperatures;        and/or    -   at relatively low firing temperatures in comparable times.

The production of shaped ceramic products, such as refractory bricks,can comprise the following steps:

-   -   production of a homogenous ceramic mix, in particular molding        mix, from refractory ceramic particles and ceramic binder;    -   optionally addition of a reactive aluminum oxide or of an        Al-containing substance; optionally addition of water or another        binder and homogenization of the ceramic mixture or molding mix;    -   optionally addition of additives and further homogenization of        the mixture or molding mix;    -   optionally, additives which perform specific functions in the        finished bricks are mixed into the mixture. Suitable additives        are for example metal powders which improve the oxidation        stability of a non-oxide ceramic product, in particular of a        ceramic refractory material;    -   pressing of the homogenous refractory molding mix into defined        brick shapes. Compression pressures≧100 MPa and ≦200 MPa are        preferred;    -   drying and/or annealing of the pressed bricks at        temperatures>50° C.; and/or firing of the dried and annealed        bricks at temperatures≧400° C.

The production of the unshaped refractory products according to theinvention can be performed at the refractory producer's works or on siteat the refractory user's works, preferably in the following steps:

-   -   production of a homogenous ceramic mix;    -   optionally addition of an active aluminum oxide or of an        Al-containing substance;    -   optionally addition of a binder, additives and/or water and        homogenization of the mechanical mixture;    -   optionally addition of additive substances and further        homogenization of the mechanical mixture.

As required, additives which perform specific functions in the finishedmolding mixes are mixed into this mixture. Examples of additivesubstances are metal powders and non-oxide materials such as carbon,carbides, nitrides, silicides, metal fibers, plastic fibers or carbonfibers, which further improve the oxidation resistance, strength, dryingbehavior, corrosion resistance and/or the temperature change resistanceof the ceramic product.

Ceramic mixes, in particular homogenous ceramic mixes, can be processedinto a ceramic product, including refractory materials, monolithicrefractory linings etc. by means of techniques common in refractorytechnology, such as pressing, casting, vibration, spraying, concretespraying, ramming and the like.

From the molding mixes according to the invention, such as refractorymolding mixes, prefabricated products can be produced. For this themolding mixes produced as described above are introduced into a metal orwood or plastic mold. By subsequent vibration, ramming, compression andthe like, the mix can be further compacted. After curing of the mix, theprefabricated product is released from the mold and dried and/orannealed at 30° C. to 200° C. As required, the dried or annealedprefabricated product can be fired. The firing conditions essentiallydepend on the chemical and mineralogical composition of the refractorymix and on the shape and geometry of the product. As a rule, a firing attemperatures 1600° C. is sufficient. After drying, annealing and/orfiring, the ceramic prefabricated product according to the invention, inparticular refractory materials, are ready for use.

The degree of curing depends on the shape of the ceramic product. In anycase, the ceramic molded body is cured until it has the strengthnecessary for avoidance of a shape change during the firing process.

The shaped and unshaped ceramic products according to the invention,such as refractory materials can be used in the furnaces and plants ofthe nonferrous metal industry, steel industry, cement industry, glassindustry, waste incineration industry and the like.

Although the organo-modified siloxanes according to the invention of theceramic binder are preferably suitable as binders for ceramic mixes,their use is not so limiting. For example, the organ-modified siloxanescan also be used in casting and pressing compounds, in coating mixes forelectrical insulators and in protective coating mixes for metalsurfaces.

A further object of the present invention relates to the ceramicproduct, in particular dimensionally stable ceramic product, itself.

It has been found according to the invention that through the use of thebinder products made of ceramic powder that are dimensionally stable canbe obtained at room temperature or temperatures of <30° C. and processtimes of several hours or days. Such ceramic products can possess goodcold crushing strength.

Particularly preferred ceramic products are refractory ceramic products.

The ceramic product can be shaped or unshaped.

According to the invention, dimensionally stable ceramic productsmanufactured under a compression pressure of 100 MPa can have a coldcrushing strength of ≧15 MPa after a heat treatment at 100° C. to ≦1000°C., preferably ≦700° C. for 2 hours.

The production and the properties of the products according to theinvention will be illustrated below on the basis of some examples whichfollow herein below.

The liquid, organo-modified siloxane compounds A to D of the binderaccording to the invention were produced according to the state of theart, as described for example in DE-A1 33 12 911, EP-A1-0 124 748 and inNoll, Chemie and Technologie der Silicone [Chemistry and Technology ofthe Silicones] (1968), Verlag Chemie. The symbols in the following tablerelate to those described above for formula (I).

Compound a b R¹ R² A 1.0 0.9 methyl ethyl B 1.0 0.4 methyl ethyl C 1.01.2 methyl ethyl D 1.9 0.1 methyl ethyl

Example 1 Binding Strength in Corundum Bricks

A high purity sintered alumina, T60 obtainable from the firm ALMATISGmbH in Ludwigshafen, with the following grain size composition:

Coarse-grained 1-2 mm 50 wt. % Medium-grained 0.2-0.5 mm 10 wt. % Flour<0.1 mm 40 wt. %was homogenously mixed with 4 wt. parts of compound A. For comparison, amolding mix was produced with 4 wt. parts of sulfite liquor (withoutcompound A). Test pieces were made from the mixtures under a compressionpressure of 100 MPa and then fired at 600° C. and 1500° C. for 2 hrs.After firing, the test pieces had the following characteristics:

With Without compound A compound A 600° C. 1500° C. 600° C. 1500° C.Cold crushing strength (MPa) >50 >100 <5 <25 (as per DIN EN 993-1)

The differences in the development of the cold crushing strengthdepending on the firing temperature in samples with and without compoundA are shown in FIG. 1.

The addition of compound A causes an enormous rise in the strength ofthe ceramics.

Example 2 Binding Strength of Different Compounds

A high purity sintered alumina, T60 obtainable from the firm ALMATISGmbH in Ludwigshafen, with the following grain size composition:

Coarse-grained 1-2 mm 50 wt. % Medium-grained 0.2-0.5 mm 10 wt. % Flour<0.1 mm 40 wt. %was homogenously mixed with 4 wt. parts of compound A, B, C and Drespectively. Test pieces were made from the mixtures under acompression pressure of 100 MPa and then fired at 600° C. for 2 hrs.After firing, the test pieces had the following characteristics:

Compound A B C D Cold crushing strength (MPa) >50 >80 >60 >10 (as perDIN EN 993-1)

The addition of compounds A, B and C causes a large increase in thestrength of the corundum bricks. The compound D develops an increasedbinding strength or strength of the corundum bricks after firing at 600°C.

Example 3 Binding Strength of an Aqueous Emulsion

A high purity sintered alumina, T60 obtainable from the firm ALMATISGmbH in Ludwigshafen, with the following grain size composition:

Coarse-grained 1-2 mm 50 wt. % Medium-grained 0.2-0.5 mm 10 wt. % Flour<0.1 mm 40 wt. %was homogenously mixed with 5 wt. parts of a 50% aqueous emulsion ofcompound B. For comparison, a molding mix was produced with 4 wt. partsof sulfite liquor (without compound B). Test pieces were made from themixtures under a compression pressure of 100 MPa and then fired at 600°C. and 1400° C. for 2 hrs. After firing, the test pieces had thefollowing characteristics:

With emulsion of Without compound B compound B 600° C. 1400° C. 600° C.1400° C. Cold crushing strength (MPa) >10 >25 <5 <20 (as per DIN EN993-1)

The aqueous emulsion of compound B is suitable as a binder for corundumbricks.

Example 4 Effect of Firing Time on Binding Strength in Corundum Bricks

A high purity sintered alumina, T60 obtainable from the firm ALMATISGmbH in Ludwigshafen, with the following grain size composition:

Coarse-grained 1-2 mm 50 wt. % Medium-grained 0.2-0.5 mm 10 wt. % Flour<0.1 mm 40 wt. %was homogenously mixed with 4 wt. parts of compound B. Test pieces weremade from the mixtures under a compression pressure of 100 MPa and thenfired at 1200° C. for 2, 6 and 10 hrs. After firing, the test pieces hadthe following characteristics:

Firing time at 1200° C. 2 hrs 6 hrs 10 hrs Cold crushing strength(MPa) >90 >100 >100 (as per DIN EN 993-1)

The duration of the firing process has no significant effect on thestrength of the corundum materials with addition of compound B.

Example 5

Effect of Compound B as Function of Concentration

A high purity sintered alumina, T60 obtainable from the firm ALMATISGmbH in Ludwigshafen, with the following grain size composition:

Coarse-grained 1-2 mm 50 wt. % Medium-grained 0.2-0.5 mm 10 wt. % Flour<0.1 mm 40 wt. %was homogenously mixed with 2, 4 and 10 wt. parts of compound B. Testpieces were made from the mixtures under a compression pressure of 100MPa and then fired at 600° C. for 2 hrs. After firing, the test pieceshad the following characteristics:

2% 4% 10% Compound B Compound B Compound B Cold crushing strength(MPa) >40 >60 >50 (as per DIN EN 993-5)

Example 6 Improvement in Binding Strength by Addition of an Active Al₂O₃

A high purity SiC raw material, SiC dunkel/dark, obtainable from thefirm ESK-SiC GmbH in Frechen, with the following grain size composition:

Coarse-grained 1-2 mm 50 wt. % Flour <0.06 mm 50 wt. %was homogenously mixed with 4 wt. parts of compound A. For comparison, amixture was also produced with 10 wt. parts of Micro-Al₂O₃ powder,calcined alumina CTC 50, obtainable from the firm ALMATIS inLudwigshafen, without compound A. Test pieces were made from themixtures under a compression pressure of 100 MPa and then fired at 600°C. and 1500° C. for 2 hrs. After firing, the test pieces had thefollowing characteristics:

Without With aluminum oxide aluminum oxide 600° C. 1500° C. 600° C.1500° C. Cold crushing strength >20 >70 >40 >120 (MPa) (DIN EN 993-5)

The addition of a reactive aluminum oxide contributes to a considerableincrease in the material strength.

Example 7 Binding Strength in Magnesia Bricks

A high purity MgO sinter, NEDMAG, obtainable from the firm NedMagIndustries B.V. in Veendam, Netherlands, with the following grain sizecomposition:

Coarse-grained 1-2 mm 50 wt. % Medium-grained 0.2-0.5 mm 10 wt. % Flour<0.1 mm 40 wt. %was homogenously mixed with 4 wt. parts of compound A. For comparison, amolding mix was produced with 4 wt. parts of sulfite liquor withoutcompound A. Test pieces were made from the mixtures under a compressionpressure of 100 MPa and then fired at 600° C. and 1500° C. for 2 hrs.After firing, the test pieces had the following characteristics:

With Without compound A compound A 600° C. 1500° C. 600° C. 1500° C.Cold crushing strength >35 >40 <5 <25 (MPa) (DIN EN 993-5)

The addition of compound A also causes a considerable increase instrength in basic MgO bricks.

Example 8 Binding Strength in Corundum Bricks Containing Graphite

A high purity sintered alumina, T60, obtainable from the firm ALMATISGmbH in Ludwigshafen, with the following grain size composition:

Coarse-grained 1-2 mm 50 wt. % Flour <0.1 mm 40 wt. % Graphite, flakes<0.2 mm 10 wt. %was homogenously mixed with 4 wt. parts of compound B. For comparison, amolding mix was produced with 4 wt. parts of sulfite liquor withoutcompound B. Test pieces were made from the mixtures under a compressionpressure of 100 MPa and then fired in air at 600° C. and 1500° C. for 2hrs. After firing, some of the test pieces were cut through in themiddle.

The size of the black core (unoxidised graphite) relative to the wholecross-section area served as a measure of the oxidation stability.

After the firing, the test pieces had the following characteristics:

With Without compound B compound B 600° C. 1500° C. 600° C. 1500° C.Cold crushing strength (MPa) >15 >30 <3 <5 Unoxidised graphite (%) ≈100<15 ≈100 ≈0

The addition of compound B also imparts considerable strength to thecarbon-containing corundum bricks. In addition, the tests showed thatcompound B improves the oxidation resistance of the carbon.

Example 9 Binder for Alumina Castable

Mixtures with the following grain size composition were prepared:

Sintered alumina, T60, coarse-grained 1-2 mm 35 wt. % Sintered alumina,T60, fine-grained <45 μm 35 wt. % Calcined alumina, CTC 50, <15 μm 30wt. %

All raw materials are obtainable from the ALMATIS GmbH in Ludwigshafen.1.5 wt. parts of compound A and 12 wt. parts of water were added to themixture. After homogenization, a self-flowing alumina castable wasformed. Test pieces from the mixture were cast in a plastic mold anddried for 24 hrs at 80° C. The test pieces were then fired at 600, 800,1000 and 1500° C., for 2 hrs.

After firing, the test pieces had the following characteristics:

600° C. 1000° C. 1200° C. 1500° C. Cold crushingstrength >80 >80 >140 >220 (MPa) (DIN EN 993-5)

The alumina castable with a relatively small addition of compound A wascharacterized by high strength.

Example 10 Alumina Ramming Mix

Mixtures with the following grain size composition were prepared:

Sintered alumina, T60, coarse-grained 1-2 mm 50 wt. % Sintered alumina,medium-grained 0.2-0.5 mm 10 wt. % Sintered alumina, T60, flour 40 wt. %

All the raw materials are obtainable from the ALMATIS GmbH inLudwigshafen. 5 wt. parts of compound C were added to the mixtures.After homogenization, the molding mix was compacted in a steel mold byimpacts. Test pieces thus produced were then fired at 600° C. and 1500°C. for 2 hrs. After firing, the test pieces had the followingcharacteristics:

600° C. 1500° C. Cold crushing strength (MPa) >50 >70 (DIN EN 1402-6)

Compound C was also very suitable as a water-free binder resin for theproduction of ramming mixes.

While the invention has been described herein with reference to specificembodiments, features and aspects, it will be recognized that theinvention is not thus limited, but rather extends in utility to othermodifications, variations, applications, and embodiments, andaccordingly all such other modifications, variations, applications, andembodiments are to be regarded as being within the spirit and scope ofthe invention.

What is claimed as new is:
 1. A process for the production of shapeddimensionally stable ceramic products which comprises: a) mixing aceramic binder with a ceramic powder to create a molding mix, saidceramic binder comprising at least one liquid organo-modified siloxanecompound, wherein the at least one organo-modified siloxane compoundcontains organoalkoxy-siloxane units according to general formula (I)

wherein R¹=an alkyl radical, an aryl radical or a mixture thereof, R²=H,an alkyl radical with 1 to 4 carbon atoms or a mixture thereof, a≧0 and≦2, and b>0 and ≦3, with the proviso that a+b≧1 and ≦4; and b)consolidating the molding mix obtained from step a) by one of pressuretreatment and heat treatment, whereby a dimensionally stable ceramicproduct is obtained.
 2. The process as claimed in claim 1, wherein saidceramic binder is contained in the molding mix in a weight proportion of0.01 wt. % to 70 wt. % based on the total weight of the ceramic powder.3. The process as claimed in claim 1, wherein the molding mix obtainedfrom step a) is applied onto a dimensionally stable support.
 4. Theprocess as claimed in claim 1, wherein a further additive substanceand/or binder is added to the ceramic powder.
 5. The process as claimedin claim 1, wherein the consolidating comprises drying at a temperatureof 50° C. to <200° C.; and/or annealing at a temperature of ≧200° C. to<1,000° C.; and/or firing at a temperature of ≧1,000° C.
 6. A processfor the production of unshaped ceramic products comprising the followingsteps: a) mixing a reactive liquid ceramic binder with a ceramic powder,said reactive liquid ceramic comprises at least one liquidorgano-modified siloxane compound, wherein the at least oneorgano-modified siloxane compound contains organoalkoxy-siloxane unitsaccording to general formula (I)

wherein R¹=an alkyl radical, an aryl radical or a mixture thereof, R²=H,an alkyl radical with 1 to 4 carbon atoms or a mixture thereof, a≧0 and≦2, and b>0 and ≦3, with the proviso that a+b≧1 and ≦4; b) optionallyadding additives, auxiliary agents and/or additive substance and/orother binders; and c) manufacturing a ceramic mix.
 7. The process asclaimed in claim 6, wherein the reactive liquid ceramic binder iscontained in the ceramic material in a weight proportion of 0.01 wt. %to 70 wt. % based on the total weight of the ceramic powder.